Analog-to-digital converters which are based on a sigma delta architecture are in particular employed in measuring technology. Sigma delta analog-to-digital converters comprise one or a plurality of integrator stages. A digital output value of the analog-to-digital converter is often corrupted by an offset error. The offset error can usually be attributed to an offset error already contained in the analog input signal on the one hand and to an offset error generated in the analog-to-digital converter on the other hand.
One way of eliminating an offset error in the analog input signal is introduced in the data sheet HAL 805 by the company Micronas. The HAL 805 is a magnetic field sensor comprising a Hall plate having chopped offset compensation and an analog-to-digital converter. The offset compensation is based on chopping the first integrator stage with a full offset signal. Disadvantageous demodulation effects and alias effects, however, are formed here and the signal-to-noise ratio deteriorates. Additionally, the area requirement of the analog-to-digital converter increases due to a first very large integrator stage required. In chopping, the signal to be chopped is usually to be modulated by a square-wave signal. The result is an offset error appearing, on average, as a square-wave signal.
WO 0203087 A1 refers to a pre-amplifier having error feedback. The solution suggested, however, is of advantage in that an analog signal can only be subjected to an analog-to-digital conversion downstream of the pre-amplifier described and after a subsequent demodulation. Additionally, the pre-amplifier circuit increases the area requirements and the current consumption. Another disadvantage is the delay time caused by the pre-amplifier having error feedback.
IEEE Journal of Solid-State Circuits, Vol. 31, MO. Dec. 12 1996, “A 0.2-mW CMOS Sigma-Delta Modulator for Speech Coding with 80 dB Dynamic Range”, by Eric J. van der Zwan and E. Carel Dijkmans, mentions demodulation effects (alias) in chopped input integrators. A considerable disadvantage, however, is the fact that offset errors of the input transistors are not eliminated.